In most cases, we use stainless steel for the cases of our wristwatches. Depending on the occasion or purpose, we also equip selected models with other case materials: such as the Seebataillon GMT with its light titanium case or the Terrasport IV BRONZE, whose case is made of aluminum bronze.
The cases of most of our watches are made of 316 L stainless steel. This is also used for medical instruments and therefore called surgical steel. Due to its corrosion resistance and other positive properties, stainless steel is used for high quality watch cases.
Stainless steel 316L is an alloy consisting mainly of iron. Chromium (17%), nickel (10%) and molybdenum (2%) are added to the steel (iron-carbon alloy with a carbon content of max. 2%) to achieve the good material properties. The low nickel content is harmless for the wearing comfort, because it is firmly bound in the alloy and is not released to the skin. Stainless steel 316 L is therefore very skin-friendly.
The hardness grade for the cases is approx. 210 HV (Vickers hardness). This makes stainless steel watches well suited for daily wear. Unfortunately, a stainless steel case is nevertheless not completely insensitive to scratches, depending on how strong the mechanical impact is. However, due to the good polishability, the cases shine like new again after a service.
Titanium is used in the current collection for the Seebataillon GMT and Lunova Tag/Datum. With the same amount of material, titanium is around 40 percent lighter than stainless steel. Nevertheless, it is very hard, highly resilient and, above all, resistant to seawater, as it does not oxidize on contact with liquids. These properties were particularly important in the development of the Seebataillon GMT. After all, the mission watch had to be very robust and still offer a high level of wearer comfort.
Another advantage of titanium is its anti-allergic properties. For people who value a nickel-free watch case, cases made of titanium and its alloys are an excellent alternative. For one thing, they are completely free of nickel – for another, titanium surfaces have a protective oxide layer that does not allow any reaction with the skin.
Up to now, titanium has had to put up with one small point of criticism with regard to its appearance for elegant timepieces – apart from the very elaborate processing of the robust material. The metal tends to have a dark, matte-gray color, which was very well suited to rugged watches – but not suitable for the elegant “Sunday watch.
The Lunova Tag/Datum attempted to use a titanium case for a elegant watch. A special polishing process enables us to give the titanium a surface that is almost identical to polished stainless steel. In this way, the Lunova Day/Date impressively proves that a functional titanium case can also shine with the utmost elegance.
For watch cases, titanium is used as pure titanium (99 percent titanium) or as an alloy. Pure titanium is used for the titanium classifications grade 1 and grade 2, which do not contain any alloyed components. For a robust operational watch like the Seebataillon GMT, we have chosen the material according to the stress. We use titanium grade 2 for the middle part of the case, titanium grade 5 is used for the screwed back. Titanium Grade 5 is characterized by an even higher mechanical strength, which is achieved by adding aluminum and vanadium.
Gold has many exciting properties: In addition to its rarity, its unusually high weight is particularly fascinating. In addition, there is its warm tone and its everlasting luster, since the precious metal does not corrode. Finally, it can be worked mechanically very well, so gold has been used for jewelry and ritual objects since time immemorial.
Pure gold (24 carats/999 gold) is rarely considered for watch cases, as it would be too soft and susceptible to scratching in this form. However, gold can be combined with other metals to form very advantageous alloys. This results not only in greater hardness of the material, but also in very aesthetic shades. In the periodic table, gold belongs to the copper group with copper and the precious metal silver. These are also the metals with which gold is usually alloyed.
18-carat or 750 rose gold, for example, contains 75% fine gold, more than 20% copper and some proportions of silver. The case of the Robert Mühle Auf/Ab GOLD was made from this alloy. 18-carat yellow gold, on the other hand, is used in the Teutonia IV Edition Gold: the alloy consists essentially of 75% fine gold and equal parts copper and silver (approx. 12.5% each).
Mühle watches with solid gold cases are as valuable as they are rare timepieces. This is also ensured by the high fine gold content of 47 grams for the Teutonia IV Lady GOLD and 67 grams for the Teutonia IV Kleine Sekunde GOLD.
There is a total of around 30 billion tons of gold in the earth’s crust. However, it is very difficult to extract the precious metal from it, since there are only about 4 milligrams of gold in 1000 kilograms of rock. It is assumed that until today only 100,000 tons of the existing gold have been mined or found. Therefore, gold – apart from its aesthetics and imperishability – is an extremely sought-after and valuable metal.
Bronze is an alloy with a copper content of at least 60 percent and is a very old material. Tin bronze, e.g., is already known from about 3500 BC and thus probably one of the first alloys produced by humans. To this day, bronze is the preferred material for casting bells or for works of art – and for some years now also for wristwatches with a particular individual character.
As an alloy, bronze consists largely of copper mixed with other metals. The second largest component of the alloy – such as aluminum – is included in the name. Particularly in ship and yacht building, bronze is a traditionally used material with aluminum. It is used, for example, for the manufacture of propellers, as it is equally resistant to fresh and saltwater.
The cases of our bronze models are also made of aluminum bronze: from the S.A.R. Rescue-Timer BRONZE from 2017 to the Yacht-Timer BRONZE from 2018 to the current Terrasport IV BRONZE. We chose this case material for the limited special editions because it changes a little bit every day and makes each watch an individual one-of-a-kind piece. This is because the bronze of the cases forms a characteristic patina over time.
We deliver timepieces with bronze cases in specially protected vacuum packaging. This prevents the case from patina formation until the new owner takes delivery of his watch. The case changes as soon as the watch is taken out of the vacuum packaging and worn or exposed to environmental influences. At first, the case becomes somewhat duller, then darker, and gradually acquires a slightly greenish tinge.
Depending on the daily habits of the owner, the process of patination proceeds differently, so that over time a very individual, unique watch is created. You can counteract the patination with a silver cleaning cloth. Without these means, patina traces are noticeable after about 2 weeks.
During a service appointment, a bronze case can be refurbished and restored to near-new condition. This is done by cleaning the disassembled watch in an ultrasonic bath and polishing or restoring the original surface appearance. Please note that some material is always removed and refurbishment is not possible indefinitely.
